Steam turbines with nozzle section regulation, in which the first turbine stage, also called the control stage, of the steam turbine is equipped with a plurality of admission sectors, whose steam flow can be set by a specific control valve in each case are known. In such steam turbines, there are in each case at least three or more control valves.
Steam turbines without nozzle section regulation or without a control stage are also known. Such steam turbines are constructed with at least one control valve up to 180 MW, with two control valves up to 600 MW and with four control valves over 600 MW.
The turbine casings of steam turbines with a control stage are constructed differently in design terms than the turbine casings of steam turbines without a control stage.